Re: Slippery slope

: The decision has consequences that are progressively worse. For example,
: many Republicans in the U.S. are saying that those who endorse gay
: marriage are on a slippery slope. Next they'll be endorsing polygamy.
: Next they'll be endorsing .... (Such arguments are often rhetorically effective
: though logicians typically classify them as fallacious.)

If you stand at the top of a slippery slope, you may slide all the way down. It means the start of a long deterioration. Similar to Thin end of the wedge.